Descriptive Astronomy 101


The seventh planet from the Sun
Third largest of the gas giants
Diameter about four times that of Earth.
Discovered by:
Just visible to the naked eye - not originally identified as a planet.
Originally called:


Axial Tilt = 97.9°
The planet effectively spins on its side.
For part of its orbit, one pole continually faces the Sun while the other is in total darkness. Half an orbit later, the roles (and poles) are reversed.
The plane containing its rings and moons is also tilted.

Interior Structure

Solid, rocky core
Deep layer of ammonia and water icy slush
Outer layer of liquid hydrogen and helium

Odd Magnetic Field

Magnetic field is not centered on the center of the planet
Tilted 59° with respect to the axis of rotation.
It is probably generated by motion at relatively shallow depths within Uranus.
Magnetosphere is twisted by the planet's rotation into a long corkscrew shape behind the planet.


Composed of hydrogen (83%), helium (15%), methane (2%), and trace amounts of acetylene and other hydrocarbons.
Bluish color due to methane haze that absorbs strongly at red wavelengths.
Banded cloud patterns are extremely bland and faint.
Up to 18 distinct cloud bands have been identified


A faint system of 13 narrow, elliptical-shaped rings.
Composed of dark dust and rocks up to about 10 meters in diameter.
Found between 38,000 and 97,000 km.


27 known moons
Titania, 1,578 km diameter
Oberon, 1,523 km diameter
Umbriel, 1,169 km diameter
Ariel, 1,158 km diameter
Miranda, 472 km diameter

Uranus: Other Facts

Distance from Sun 19.2 AU
Distance from Sun 2,869 million km
Equatorial diameter 51,108 km
Mass (Earth=1) 14.6
Mean density 1.3 g/cm3
Axial period 17.9 hours
Axial inclination 97.9°
Orbital period 84 years
Orbital inclination 0.8°
Orbital eccentricity 0.047
Gravity at cloud-tops (Earth=1) 1.17
Escape velocity 22.5 km/s
Albedo 0.35